1. Field of the Invention
The present invention relates to a technique to inspect a defect in run-length data which is acquired by performing a RIP process on input data describing a figure to be drawn and is to be used for drawing of the figure. More particularly, the present invention relates to a technique to inspect a defect in run-length data to be used for a process of drawing a circuit pattern of e.g., a semiconductor substrate, a glass substrate for liquid crystal display, a glass substrate for photomask, a glass substrate for plasma display, a substrate for optical disk or the like (hereinafter, referred to simply as “substrate”) onto a resist directly from CAD data.
2. Description of the Background Art
With high integration and complication of semiconductor integrated circuits in recent, it is becoming indispensable to convert a business model of mass production of small varieties for e.g., DRAMs (Dynamic Random Access Memories) to that of small-quantity production of large varieties (flexible manufacturing system) for e.g., system LSIs. Further, circuit patterns of the system LSIs and the like have been miniaturized year after year and therefore the development cost has become enormous.
In pattern drawing (more specifically, pattern drawing (exposure) by photolithography) onto substrates, conventionally, a circuit pattern which is formed and compiled by a CAD system is drawn onto a film by laser to produce a photomask and the circuit pattern is transferred onto substrates by using the photomask. Photomasks which are thus produced, however, are very expensive since these are finely processed with high precision and disadvantageously not suitable for flexible manufacturing system in terms of cost.
Then, for reduction in cost for development of the system LSIs and the like, a pattern drawing system not using any photomask (specifically, a system for drawing circuit patterns onto resists directly from CAD data, which is hereinafter referred to as “direct drawing system”) has been introduced.
An apparatus for drawing circuit patterns by direct drawing system (hereinafter, referred to as “direct drawing apparatus”) performs drawing by interpreting run-length data (described by starting point positions and lengths of a plurality of line segments in a horizontal direction (or vertical direction) which is obtained by performing a RIP (Raster Image Processor) process on CAD data describing a circuit pattern to be drawn.
There is a possible case, however, where defects (in other words, differences from the description of the CAD data) are caused in the run-length data obtained by the RIP process by wrong conversion in the RIP process and the like. If the run-length data has a defect, correct drawing can not be performed. Therefore, in performing such drawing, a process to verify if correct drawing can be performed on the basis of run-length data without any defect should be performed.
In a pattern drawing system using photomask, a photomask is necessarily generated before execution of drawing. Therefore, by checking this photomask, it is possible to verify if correct drawing can be performed.
In the direct drawing system not using any photomask, however, it is impossible to inspect any defect in run-length data by using the photomask since drawing is performed without generation of the photomask. Then, in the direct drawing system, conventionally, drawing is performed onto substrates and the drawn circuit patterns are inspected. Defects are inspected, for example, by visually checking the circuit patterns on the substrates after development, or by checking images (picked-up images) obtained by imaging the circuit patterns on the substrates after development (see Japanese Patent Application Laid Open Gazette No. 2001-337041).
With this constitution, it is impossible to detect any defect in run-length data until drawing is once performed. In other words, even if the run-length data obtained by the RIP process has some defect, it is impossible to detect the defect before the execution of drawing. Therefore, a drawing process is performed on the basis of the defective run-length data and the substrates subjected to this drawing process go to waste.
In order to avoid producing such waste samples, a technique to detect any defect in run-length data before execution of drawing has been suggested. For example, suggested is a method where run-length data (for drawing) obtained by the RIP process from CAD data and run-length data (for verification) obtained from the CAD data by using an algorithm different from that of the RIP process are compared with each other, to detect any defect which occurs in the run-length data to be used for drawing (see Japanese Patent Application Laid Open Gazette No. 2004-56068).
The above constitution has an advantage that no sample goes to waste since it is possible to detect any defect in the run-length data before execution of drawing. This constitution, however, needs not only a functional part for performing the RIP process to acquire the run-length data to be actually used for drawing but also another functional part for performing a RIP process defined by an algorithm different from that of the above RIP process. In other words, a plurality of functional parts for the RIP processes are needed and a plurality of RIP processes should be performed for detection of defects. This increases the load for detection of defects and makes the processing time longer.
For these reasons, a technique to allow detection of defects in run-length data before execution of drawing with simple constitution has been sought.